Amyotrophic lateral sclerosis (ALS) is an adult onset neurodegenerative disease which specifically targets motoneurons. In 20% of familial ALS (fALS) cases, there is a specific mutation in superoxide dismutase (SOD1). Mice with mutated human SOD1, display the same pathological and phenotypical symptoms in human ALS patients and are therefore widely used as an animal model of fALS. However, the role SOD1 plays in determining motoneuron death remains unclear. A leading hypothesis is that excitotoxicity caused by an overload of calcium into the cell due to motoneuron hyperexcitability causes selective motoneuron death because motoneurons have a low capacity to buffer calcium. This proposal aims to determine the relative contribution of changes in intrinsic and synaptic motoneuron excitability between wild type and SOD1 motoneurons. Furthermore, the effect of Riluzole, the only FDA approved drug for ALS, on both intrinsic and synaptic motoneuron excitability will also be assessed. The aims of this proposal will be accomplished through the use of embryonic cultured motoneurons, neonatal spinal cord slices, and a new in vitro sacral cord preparation. The use of these preparations will allow an efficient and complete characterization of motoneuron excitability between wild type and SOD1 mice. The in vitro sacral cord preparation allows intrinsic and synaptic motoneuron excitability to be assessed through intracellular recordings at time points throughout development and adulthood. It also enables us to administer Riluzole at therapeutic levels and in multiple time courses to extensively characterize the effects of Riluzole over time. The neonatal spinal cord slice preparation allows intrinsic versus synaptic motoneuron excitability to be assessed using direct bath application of drugs to inhibit specific ion channels using a whole cell patch clamp configuration. Also, the direct and immediate effects of Riluzole on motoneurons can be determined. The embryonic cultured motoneurons provide a window into motoneuron abnormalities present before birth and also give us a preparation where no synaptic inputs are present. In this preparation the effects of Riluzole administered over multiple time courses on the intrinsic properties of motoneurons can be isolated. The cause(s) of motoneuron degeneration in ALS needs to be determined in order to develop novel drugs treatments and understanding differences or changes in motoneuron function will lead to specific targets for these future drugs. Furthermore, early detectable changes in motoneuron function may enable the use of pre-emptive therapies that can significantly delay or even arrest the development of the disease.